The present invention relates to pulverulent compounds of the formula NiaM1bM2cOx(OH)y, a process for producing them and their use as intermediate for producing lithium compounds for use in secondary lithium batteries.
JP10027611 A discloses the synthesis of a coprecipitated mixed hydroxide which comprises at least the two metals nickel and cobalt but is not restricted to these. The coprecipitated mixed hydroxide is processed further to give lithium mixed metal oxides as active composition for secondary lithium batteries. Coprecipitation of the elements at the stage of the intermediate makes it possible to produce a lithium mixed metal oxide which when used in secondary lithium batteries leads to an improvement in the electrochemical cycling behavior. The molar proportion of nickel in the lithium mixed metal oxides, based on the metallic elements apart from lithium, is at least 70%.
JP 11-317224 A describes the synthesis of manganese- and cobalt-doped nickel hydroxides by means of coprecipitation. The synthesis is carried out under reducing or inert conditions in order to avoid oxidation of the divalent metals. The material has high tapped densities (>1.7 g/cm3) and is used as active composition for secondary alkaline batteries.
US 2002/0053663 A1 claims a coprecipitated nickel-cobalt-manganese hydroxide which has a tapped density of at least 1.5 g/cm3. The coprecipitated mixed hydroxide serves as intermediate for the synthesis of lithium-nickel-cobalt-manganese oxides (LNCMOs). The processes described as “conventional” in the patent do not enable mixed hydroxides having a high tapped density to be produced. The high tapped density of the mixed hydroxide is of such great importance since it has a positive effect on the tapped density of the end product, which in turn influences the volumetric energy density in a secondary lithium battery. The examples disclose powders whose tapped densities are from 1.71 to 1.91 g/cm3. The average particle size of the powders is 5-20 μm.
Mixed hydroxides having high tapped densities were able to be achieved in US 2002/0053663 A by carrying out the precipitation either under inert conditions or even under reducing conditions.
US 2003/0054251 A1 describes an optimized route to the synthesis of nickel- and manganese-containing mixed oxides or mixed hydroxides as intermediates for the cathodic active composition in secondary lithium batteries. The main idea of this invention is to pretreat the coprecipitated mixed hydroxides (e.g. of the metals Ni, Co, Mn) mentioned in the literature thermally at 300-500° C. to obtain a “dry precursor” before the actual furnace process. This “dry precursor” is then admixed with a lithium component and reacted by means of ignition to form the LNCMO. If the dried intermediate described is used instead of an (undried) mixed hydroxide, an end product which has a higher product constancy than materials in which the undried mixed hydroxide was used is obtained according to this document. The product constancy of the materials was determined by making twenty batteries from each material and evaluating the variation in the capacity decrease between the third and three hundredth electrochemical cycle for these twenty batteries.
WO 2004/092073 A1 is likewise concerned with mixed metal intermediates for LNCMO materials. As in US 2003/0054251, an ideal intermediate for the synthesis of LNCMOs is sought here. US 2003/0054251 is, inter alia, mentioned as prior art therein. Since the thermal treatment of the intermediate as described in US 2003/0054251 is very complicated, an oxidation of the coprecipitated Ni—Co—Mn hydroxide to an Ni/Co/Mn oxyhydroxide is proposed as an alternative.
WO 2007/019986 discloses partially oxidized nickel mixed metal hydroxides (NCMOs), a process for producing them and their use as intermediate for producing cathode material for secondary lithium batteries.
The nickel mixed metal hydroxides are characterized in that they have a tapped density of greater than 1.7 g/cm3, preferably greater than 1.9 g/cm3, and an average particle size of the secondary particles of from 2 to 30 μm. The normalized width of the particle size distribution is less than 1.8.
The NCMOs are prepared here by precipitation of metal salts by means of alkalis and subsequent partial oxidation in a further reactor. A high tapped density of the partially oxidized NCMO is said to be achieved in this way.
The nickel mixed metal hydroxides prepared according to the prior art cited are used as starting materials for producing secondary lithium batteries. Such secondary batteries have only limited suitability for use in hybrid and electric vehicles.
For both types of vehicles, rapid discharging and charging of the batteries is necessary to be able to achieve high accelerations and on braking of the vehicle to convert the kinetic energy thereof back into electric energy with a very low level of heat losses. At a given energy for a particular acceleration or braking process, the discharging/charging rate required, expressed in ±Δ total capacity/Δt, is lower the higher the total capacity of the battery. Thus, a very high volume capacity of the battery is sought not only for space and cost reasons but also for electrical reasons. In the case of a pure electric vehicle, this is also absolutely necessary because the capacity naturally determines the operating range and this is absolutely critical to the marketability of such vehicles.